Security Cameras and Surveillance: A Beginner’s Guide (Part 1)
You already know that protecting your home and your family are important and security cameras play a pivotal role in achieving that, but you are not quite sure of the type you want. The market is awash with all sort of variants. How do you choose which one is ideal? What other factors do you consider besides your budget? Here at PhilipCosby we are determined to help you solve that puzzle.
Security cameras basically come in two technologies namely ‘Analogue’ and ‘Digital’
Analogue cameras are based on television technology using CCD sensors (Charged-Coupled Device) a light-sensitive integrated circuit that stores images such that each pixel in the image is converted to an electrical charge the intensity of which is related to a colour in the colour spectrum.
Digital cameras make use of the CMOS sensors (Complementary Metal-Oxide Semiconductor) with software embedded in the camera. Digital cameras have become extremely common as the prices have come down. One of the drivers behind the falling prices has been the introduction of the CMOS image sensors. CMOS sensors are much less expensive to manufacture than CCD sensors. Both CCD (Charge-Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) image sensors start at the same point, they have to convert light into electrons.
Analogue and Digital cameras come in various models such as Box, Bullet, Dome, Day/Night, Infrared as well as Pan-Tilt-Zoom (PTZ) all have different lenses. It is interesting to note that not all camera types and models are suitable for every light or weather condition. A very important issue we will be dwelling on today is the use of wrong lenses. Using the wrong lenses can be detrimental to your safety. Choosing wrong lenses is one of the commonest mistakes in CCTV installation across the country. This normally leads to situations where people appear too small for any meaningful recognition.
To observe a person at 50% you can only view an area the width of two car park spaces (Approximately 4 meters) The most popular lens sold to customers in the fixed 3.6 millimeter , which gives you a wide angle view of 70 degrees but can only provide a facial recognition of 3.2 meters so if your camera is located at a height of 5 meters you are depending on an intruder bringing a ladder and climbing up in front of the Camera in order to be recognized! Generally, a 3.6-millimeter lens will only enable you to either observe or detect a person.
The table below gives the angle of view and recognition distance of some popular lens formats.
It is important to use the right lens for the right light conditions and desired field of view, otherwise, the images seen and recorded will not be satisfactory. CCTV security cameras with the fixed lens are less expensive but do not offer lens choices and are therefore limited in their usefulness. One of the important factors that govern the choice of lens is Focal Length: Lenses either have a fixed or variable focal length. Manually variable focal length lenses are called Vari-Focal Camera Lenses. Electrically powered variable focal length lenses are called Zoom Camera Lenses and while they are often used in high-end video surveillance systems, they are generally too expensive for use in most systems. The focal length of a lens is usually given in Millimeters (mm) Focal lengths of most CCTV camera lenses vary from 3.6 millimetres to 16 millimetres for fixed focal length lenses, to well over 70 millimetres for zoom lenses. So what does that mean? In general, short focal length lenses (e.g. 4 millimetres) have wide fields of view. This is good for close-ups or for seeing a large area. Objects appear smaller, rapidly, as the distance from the camera increases. As lens focal length increases, the field of view narrows and more distant objects are easier to define. Please refer to table 1
If you choose the wrong lens camera, there is a 90% chance the police will not be able to make use of any crime footage that is recorded and we all know the implications of this.